Biomedical subjects

Giuseppe E Santoro

Publications and source records attributed to Giuseppe E Santoro.

6 recordsLinked to original sources

PubMed2006

Exactly quantized dynamics of classical incommensurate sliders.

We report peculiar velocity quantization phenomena in the classical motion of an idealized 1D solid lubricant, consisting of a harmonic chain interposed between two periodic sliders. The ratio upsilon(c.m.)/upsilon(ext) of the chain center-of-mass velocity to the externally imposed relative velocity of the sliders stays pinned to exact "plateau" values for wide ranges of parameters, such as slider corrugation amplitudes, external velocity, chain stiffness, and dissipation, and is strictly determined by the commensurability ratios alone. The phenomenon is explained by one slider rigidly dragging the kinks that the chain forms with the other slider. Possible consequences of these results for some real systems are discussed.

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PubMed2005

Optimization by quantum annealing: lessons from hard satisfiability problems.

The path integral Monte Carlo simulated quantum annealing algorithm is applied to the optimization of a large hard instance of the random satisfiability problem (N = 10,000). The dynamical behavior of the quantum and the classical annealing are compared, showing important qualitative differences in the way of exploring the complex energy landscape of the combinatorial optimization problem. At variance with the results obtained for the Ising spin glass and for the traveling salesman problem, in the present case the linear-schedule quantum annealing performance is definitely worse than classical annealing. Nevertheless, a quantum cooling protocol based on field-cycling and able to outperform standard classical simulated annealing over short time scales is introduced.

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PubMed2004

Quantum annealing of the traveling-salesman problem.

We propose a path-integral Monte Carlo quantum annealing scheme for the symmetric traveling-salesman problem, based on a highly constrained Ising-like representation, and we compare its performance against standard thermal simulated annealing. The Monte Carlo moves implemented are standard, and consist in restructuring a tour by exchanging two links (two-opt moves). The quantum annealing scheme, even with a drastically simple form of kinetic energy, appears definitely superior to the classical one, when tested on a 1002-city instance of the standard TSPLIB.

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PubMed2004

Strong correlations in electron doped phthalocyanine conductors near half filling.

We propose that electron doped nontransition metal phthalocyanines such as ZnPc and MgPc, similar to those very recently reported, should constitute novel strongly correlated metals. Because of orbital degeneracy, Jahn-Teller coupling, and Hund's rule exchange, and with a large on-site Coulomb repulsion, these molecular conductors should display, particularly near half filling at two electrons/molecule, very unconventional properties, including Mott insulators, strongly correlated superconductivity, and other intriguing phases.

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PubMed2003

Nontrivial fixed point in a twofold orbitally degenerate Anderson impurity model.

We study a twofold orbitally degenerate Anderson impurity model which shows a nontrivial fixed point similar to that of the two-impurity Kondo model, but remarkably more robust, as it can only be destabilized by orbital- or gauge-symmetry breaking. The impurity model is interesting per se, but here our interest is rather in the possibility that it might be representative of a strongly correlated lattice model close to a Mott transition. We argue that this lattice model should unavoidably encounter the nontrivial fixed point just before the Mott transition and react to its instability by spontaneous generation of an orbital, spin-orbital or superconducting order parameter.

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PubMed2002

Theory of quantum annealing of an Ising spin glass.

Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. By comparing classical and quantum Monte Carlo annealing protocols on the two-dimensional random Ising model (a prototype spin glass), we confirm the superiority of quantum annealing relative to classical annealing. We also propose a theory of quantum annealing based on a cascade of Landau-Zener tunneling events. For both classical and quantum annealing, the residual energy after annealing is inversely proportional to a power of the logarithm of the annealing time, but the quantum case has a larger power that makes it faster.

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